It is well-known to protect, and control the use of, an item of content that is delivered (or communicated/transmitted) to an end user (or to a device used by an end user). However, as mobile data processing devices (such as smartphones, tablet computers, laptops, etc.) are becoming more and more prevalent and are more often than not the user's preferred device, it is important to be able to deliver items of content to such mobile data processing devices (thereby satisfying user demand) whilst at the same time ensuring a high level of security (thereby satisfying the requirements of content providers and content distributors). This is especially true given the very large number of such devices currently available and the rate at which new devices enter the market, coupled with the range of operating systems and software that such devices run, all of which make protection of content a difficult challenge.